If you upgrade GCC from a version earlier than 3.4.0 (for the 3.x series) or 4.1, you will need to run revdep-rebuild as well:

root #revdep-rebuild --library 'libstdc++\.so\.5'

Check the current version and uninstall the old version:

root #gcc --version

root #emerge --ask --depclean =sys-devel/gcc-4.4.5

这样就完成了！

GCC upgrading explained

介绍

GCC upgrading has always been mystified, with suggestions ranging from "You do not need to do anything" up to "You will need to rebuild your entire system twice". Most of this fear, uncertainty and doubt comes from the confusion surrounding ABI incompatibility. But first a quick pointer towards libtool.

libtool 和 fix_libtool_files.sh

Earlier installments of GCC on Gentoo required you to run a specific command called fix_libtool_files.sh. Some time ago, the execution of this command has been integrated in the package deployments itself (through the toolchain eclass) so there is no need for users to call this themselves anymore.

The reason we need to rebuild libtool after the upgrade of gcc versions is because of its main purpose: libtool is a toolset that aggregates platform-specific code in a generic interface, allowing applications to build against shared libraries without needing to deal with the platform specific aspects of shared libraries. To fulfill its function properly, the libtool script uses various library locations that have hard-coded gcc version information in them.

ABI changes

An ABI, or Application Binary Interface, is a set of conventions used by all tools that deal with binary representation of programs, including compilers, assemblers, linkers, and language runtime support (source: GCC Binary Compatibility). When the ABI used for binary applications and libraries is changed, you will risk getting linker errors or malfunctioning programs unless you rebuild all libraries that use C++ code.

Yes, C++, since most incompatibilities occur within the C++ ABI. If you are upgrading to GCC 4.1, or GCC 5.1, you would probably encounter ABI issues. This is also why we use the revdep-rebuild command against the libstdc++.so.5 (from GCC 3 to GCC 4.1), or libstdc++.so.6 (from GCC 4 to GCC 5.1).

The special case C++11 (and C++14)

While GCC (or more specifically, libstdc++) goes to great lengths to guarantee stability of the ABI, this guarantee does not extend to all parts of C++ within libstdc++. Formally, with versions starting from 3.4, GCC/libstdc++ only guarantees C++98/C++03 ABI stability and not more. This is crucial for packages that depend on C++11. GCC only makes C++11 ABI stability guarantees beginning with version 5.1. This means that switching (even minor) versions of gcc (say from 4.7.3 -> 4.7.4) might cause ABI breakage for binaries built from C++11 code.

Rebuilding everything

That however doesn't mean they are completely incorrect: newer GCC versions often include better support for the processors' instruction set, which might influence the performance of some applications in a positive way. Although it is expected that this improvement is generally only marginal, in some cases (especially CPU intensive applications) this might yield notable improvements.

There are also known cases where packages need to be built with the same compiler. Although these packages are usually bumped by package maintainers simultaneously (so that they are always built with the same GCC version) cherry-picking re-installs on these packages might prove to be troublesome. The various qt-* packages are a nice example on this matter.

故障排除

libstdc++.so.6: version `GLIBCXX_3.4.15' not found

在升级过程中,你或许会遇到以下面这些错误:

CODEGLIBCXX_x.y.z not found

cmake_bootstrap_28021_test: /usr/lib/gcc/i486-pc-linux-gnu/4.1.2/libstdc++.so.6:
version `GLIBCXX_3.4.11' not found